The present invention relates to elastomeric compositions having improved appearance.
More specifically, the present invention relates to elastomeric compositions comprising an elastomer and carbon black which provide the elastomeric compositions with improved visual properties, such as jetness and gloss.
Carbon blacks are generally produced in a furnace-type reactor by pyrolyzing a hydrocarbon feedstock with hot combustion gases to produce combustion products containing particulate carbon black.
Carbon blacks are generally characterized on the basis of analytical properties including, but not limited to, surface area, surface chemistry, aggregate size, and particle size. The properties of carbon blacks are analytically determined by tests known to the art, including, for example, CTAB, DBP, and tinting strength value (Tint). Carbon blacks may also be characterized by CDBP, Iodine surface area (I2No.), and nitrogen surface area (N2SA), as well as other properties.
Carbon blacks may be utilized as pigments, fillers, reinforcing agents and for a variety of other applications. For example, carbon blacks are widely utilized as fillers and reinforcing pigments in the compounding and preparation of rubber and plastic compounds. More particularly, carbon blacks are effective in the preparation of rubber vulcanizates intended for usage in preparing tires.
It is generally understood that the properties of a carbon black affect the properties of rubber or plastic compounds containing the carbon black. Thus, the properties of a carbon black will affect the properties of tire compounds containing the carbon black.
The sidewall area of passenger, light truck, medium truck, and similar tires has long been the subject of extensive cosmetic attention. Manufacturers, wholesalers, retailers, and consumers in both the tire and automotive industries place value on the visual appearance of the tire sidewall. By way of non-limiting example, tires featuring the traditional white sidewall, raised black letters, raised white letters, dual sidewall stripes, sidewall stripes of colors other than white, and outlined (in white) raised letters have all been xe2x80x9cin stylexe2x80x9d at various times and/or places.
Currently, the simple black sidewall is in style. However, with the carbon blacks and elastomers presently used in tire manufacture, the appearance of the black sidewall is diminished in two ways:
the carbon blacks used are of a very low surface area, semi-reinforcing type, which does not give an attractive appearance as discussed later. The current industry practice is to use carbon blacks having CTAB of less than about 50 m2/g in most cases. The tint of these blacks is, in most cases, about 60% ITRB.
the elastomers used in tire manufacture are traditional, unsaturated elastomers which depend upon antiozonants and antioxidants to protect them from degradation caused by exposure to the elements. These antidegradants xe2x80x9cbloomxe2x80x9d to the surface to react with the ozone and impart protection to the elastomer(s). Unfortunately, in so doing, these antidegradants turn brown, which in turn further worsens the appearance of the already dull sidewall compound.
Tire buyers combat this by washing their tires frequently, and by applying xe2x80x9ctire dressingsxe2x80x9d of various types. In fact, in North America consumers are currently spending upwards of $80 million per year to enhance the appearance of their tire sidewalls and other vehicle components.
In addition to determining the tire""s appearance, the sidewall compound must meet certain performance requirements. The major requirement is good flex fatigue, meaning that the compound must not develop any cracking, checking, splitting, or the like over the life of the tire. Two other commonly-accepted requirements are cutting/chipping resistance, and abrasion resistance, both of which help in resisting damage caused by impacts with curbs and the like. The rigor of these performance requirements varies widely with the type of tire/service that the tire will undergo.
At present, about 41 grades of carbon black are manufactured and used routinely in elastomer applications, and in particular rubber applications such as tire components. Use of these carbon blacks is generally controlled exclusively by functional considerations, i.e., the functional properties which the resulting product is desired or required to possess.
In addition, a range of carbon blacks are made for use in non-elastomer applications such as inks, paints, and plastics. In most of these applications an important function of these specialty carbon blacks is to impart an esthetically pleasing appearance to the finished product, which is often an ink or a paint. Terms such as jetness, undertone (blue or brown), and gloss may be used in describing the characteristics of such products, and characteristics imparted to inks and paints by these products.
It has now unexpectedly been discovered that certain of the specialty blacks products can enhance the appearance of elastomeric compounds, including sidewall compounds, while still satisfying critical functional criteria.
The present invention is generally directed to carbon black-containing elastomeric compositions which preferably exhibit hi gloss and jetness, combined with desirable physical properties. The compositions comprise an elastomer(s) and a specified carbon black, which is preferably furnace carbon black.
The carbon black component of the rubber composition is a furnace carbon black having an I2No of from about 80, or from about 100, preferably from about 125, more preferably from about 140 mg/g, to about 400, preferably to about 375, and most preferably to about 360 mg/g.
The carbon black may have a DBP value of at least about 50 cc/100 g, a tint value of at least about 100% ITRB, and a CTAB value of at least about 80 m2/g.
The elastomer component of the formulation of the present invention may be any suitable natural or synthetic rubber, or mixtures of these rubbers and their derivatives. The elastomer may be, but is not limited to, homo- or co-polymers of 1,3-butadiene, styrene, isoprene, isobutylene, 2,3-dimethyl-1,3-butadiene, acrylonitrile, ethylene, and propylene, SBR (including solution SBR, functional solution SBR, and/or emulsion SBR), and natural rubber. Rubbers found to have particular utility include natural rubber, butadiene rubber, and blends thereof. Non-saturated rubbers such as halobutyl, styrenated halobutyl, EPDM, and the like are also of interest, as these elastomers may allow a reduction in the use of the xe2x80x9cbrowningxe2x80x9d antiozonants/antioxidants as well.
Applications for the elastomeric compositions include, but are not limited to, the above mentioned sidewall area of passenger, light truck, medium/heavy truck tires, airplane, racing, and large xe2x80x9coff the roadxe2x80x9d tires. In these applications, the rubber compositions of the present invention may be used as veneers over the sidewall area or as the entire sidewall compound. In addition, other automotive components may benefit from an improved appearance, including components such as weather-stripping, hoses, windshield wipers, and belts. As in the tire sidewall example, the article may be made entirely from the rubber compositions of the present invention, or the present invention may simply be used as a veneer covering the otherwise exposed surface.
In addition to elastomer compositions used in the tire and automotive areas, the present invention has application to any elastomeric compositions used in environments where a glossy esthetic appearance would be desirable, regardless of the need for the functional properties which may correspondingly be obtained through practice of the present invention. Such applications may include, by way of non-limiting example, construction or building materials, such as moldings; consumer apparel, such as footwear (including without limitation sneakers, boots, and shoes); furniture guards and bumpers; and children""s toys and play equipment, such as swing seats.
Hereinafter compositions of the present invention will be discussed and exemplified in terms of rubbers; however, it will be understood that the discussion is not limited to rubbers, and is applicable to elastomers and polymers generally.
The rubber composition of the present invention generally comprises from about 20 to about 200 parts by weight of carbon black for each 100 parts by weight of rubber(s) used. (The quantification of carbon black as parts by weight per 100 parts by weight of rubber is hereinafter abbreviated as xe2x80x9cphrxe2x80x9d; thus, a composition containing 20 phr carbon black would contain 20 parts by weight carbon black per 100 parts by weight rubber.) It is, however, preferred to use from about 25 to about 125 phr of carbon black, and especially preferred is a composition comprising from about 25 to about 75 phr of carbon black.
The rubber compositions may include conventional additives such as curing agents, processing additives, hydrocarbon oils, accelerators, coagents, antioxidants and the like.